This week, surgeons at Emory University in Atlanta implanted a second dose of neural cells into a patient's spinal cord, part of an experimental treatment aimed at slowing the progression of ALS, or Lou Gehrig's disease. The patient, Ted Harada, is the third person this summer to receive a second dose as part of the trial. The cells are produced by a Rockville, Maryland-based company called Neuralstem that isolates stem cells from the brain and spinal cord of aborted fetuses. The company is also targeting other major central nervous system conditions with its cell therapy platform, including spinal cord injury, ischemic spastic paraplegia, chronic stroke, and brain cancer.

ALS gradually destroys the connections between the spinal cord and motor neurons, eventually robbing patients of all ability to move. The hope is that the cells injected into the spinal cord will provide support, perhaps by releasing growth factors, and prevent motor neurons from dying. "They nurture the dying motor neurons back to health or make them healthier and slow down the degenerative process," says Richard Garr, CEO of Neuralstem.

"We have found that the procedure is extremely safe," says Eva Feldman, a neurologist at the University of Michigan and the lead investigator of the trial. "In a subset of patients, we seem to see that the disease is no longer progressing," but it is too early to know if the result from that small number of patients is meaningful, she says.

In his first surgery, Harada received 10 injections, each containing about 100,000 cells, on the sides of his lower spinal cord. After the procedure, he was able to move his limbs with strength and dexterity that surpassed his abilities before the treatment. While some ALS patients may see brief periods of small improvements or stabilization, this degree of recovery is unheard of. In the last few months, Harada says his abilities have slowly been regressing, although at a slower pace than before the treatment.

In this week's procedure, instead of injecting cells into Harada's lower spine, a surgeon will place the cells into his upper spinal cord, a region that holds the large nerve cells that control breathing. Since ALS patients usually die of respiratory arrest, the researchers hope the treatment will protect motor neurons in the upper spinal cord and prevent or slow the loss of lung function.

Neuralstem's cells are somewhat different than typical stem cells, in that they have a defined fate. By taking cells from a fetus of a particular gestation stage, the company generates cells that are still able to divide but turn into a specific cell type, such as a spinal cord cells. This unique property of Neuralstem's cells enables the company to test potential drugs in specific central nervous system cell types in culture dishes. The company is currently searching for drugs that can protect and nurture neurons from the hippocampus, a part of the brain critical for forming and storing memories.

Another ALS trial, under way at the Mayo Clinic, is testing a treatment that injects a patient's own stem cells, isolated from fat tissue, into his or her spinal fluid. So far, two patients have undergone the procedure. Like the Emory trial, the Mayo Clinic study is focused on safety. Although such stem cell treatments are still quite new and carry risks, the dire situation of ALS patients shifts the balance of risk and benefit. "When you have a disease like ALS, where the average survival is two to three years after diagnosis and it is uniformly fatal, investigators and the FDA think it's ethical to try these more desperate approaches that carry potentially higher risk," says Anthony Windebank, a neurologist who heads the Mayo trial.

If the procedure proves safe, one of the next steps for the field would be to genetically modify the cells to produce specific growth factors likely to prevent motor neuron death, says Windebank. "If there's any sign of efficacy with these approaches, then translation into the clinic would happen very rapidly."